url : website to check
working_directory : fetched data will be downloaded
varnishlog_binary_path : path to varnishlog
email_address : email address to send result
smtp_host : smtp host to use
debug_level : log level of this utility (debug =>very verbose,
info=>normal,
warning=>nothing)
header_list : Key == Header id.
value: if equals to True, it means that header needs to be present in RESPONSE
if it is a tuple, the Header value must sastify at least one of the proposed values
erp5_extension_list: Optional section.
prohibited_file_name_list: which check that any links redirect to prohibited forms
like WebSection_viewAsWeb, Base_viewHistory, list, ...
prohibited_folder_name_list: usefull to detect that links does not redirect to
specified modules like, web_page_module, document_module, ...

This utility requires wget => 1.12
And a callable varnishlog.
The utility must be run on same server where varnish is running.

web_checker reads varnishlogs to detect if a Query goes to the backend.